1. Field of the Invention
The present invention relates to a digital multi-media device such as a digital video device and an arrangement and method which allows the device to communicate with another device on a common bus.
2. Description of the Related Art
In the field of digital video processing, it is known to code digital video signals such that special processing is needed in the receiver to be able to reproduce the video signals. In particular, it has been proposed to provide a Conditional Access Module which can perform all of the descrambling and other conditional access functions of the digital TV receiver. This allows conditional access and signal decoding functions to be separated from a host receiver, such that a generic digital TV receiver can operate with many different conditional access systems in different Conditional Access Modules.
To allow communication between a Conditional Access Module and a digital TV receiver, a Common Interface has been proposed and standardized by CENELEC (EN50221 Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications). This standard Common Interface defines a transport stream interface in which various virtual channels are time multiplexed and a Command Interface over which various additional command data are sent. The Common Interface thus allows connection of a Conditional Access Module to a digital TV receiver or indeed any other digital video device.
As a basis for the present invention, it is now recognised that it would be advantageous to provide a Conditional Access Module on a local network of digital multi-media devices including audio and video devices, such that the various functions available in the Conditional Access Module can be provided to all of the devices on the network.
A standard has been proposed for connecting together various digital video devices on a local network. In particular, IEEE 1394 is a 1995 IEEE standard for a high performance serial bus and defines a bus, which will be referred to as an IEEE 1394 Serial Bus, for connecting together various digital consumer audio/visual products.
The IEEE 1394 specification defines a physical connector, electrical signalling and a set of link and transaction protocols allowing the serial bus to self configure and carry audio, video and control information efficiently.
A further set of additional protocols have also been defined to carry MPEG data and provide control mechanisms between different items of equipment on the IEEE 1394 Serial Bus. These protocols are defined in the specification xe2x80x9cDigital Interface for Consumer Electronic Audio/Video Equipmentxe2x80x9d (IEC 1883).
The IEEE 1394 specification defines mechanisms and protocols to carry two types of data, namely asynchronous and isochronous data.
Asynchronous data generally has no requirements on the transport mechanism regarding time, for example the jitter imposed or the delay in transmission. This data can be used for instance for file data or general command and status data.
On the other hand, isochronous data has strong requirements for low jitter and a fixed or bounded delay for transmission and may be used for MPEG coded audio and video data.
In view of the developments with the IEEE 1394 Serial Bus, it is now considered to connect a Conditional Access Module to a number of different digital multi-media devices such as audio and/or video devices using the IEEE 1394 Serial Bus. Unfortunately, however there are significant problems in implementing such a system. IEEE 1394 related protocols have been developed that are intended for use with streams of single channel MPEG data and its own protocols are provided for various command data. In particular, the Conditional Access Common Interface and the IEEE 1394 serial bus have set different standards.
A first aspect of the present invention concerns the problem that, for the Common Interface, the transport stream sent to the Conditional Access Module includes all of the virtual channels and hence takes up a significant amount of the bandwidth available over the IEEE 1394 Serial Bus.
The first aspect of the present invention also deals with the problem that it is often not sufficient to send to a Conditional Access Module merely the virtual channel which it requires for descrambling, since other data in the transport stream may be required by the Conditional Access Module.
A second aspect of the present invention concerns implementing the Transport Stream Interface of the Common Interface over an IEEE 1394 Serial Bus so that the transport stream data of the interface may be communicated over the IEEE 1394 Serial Bus.
A third aspect of the present invention concerns implementing the Command Interface over the IEEE 1394 Serial Bus.
The fourth aspect of the present invention concerns implementing the Command Interface over the IEEE 1394 Serial Bus.
According to the first aspect of the present invention, there is provided a digital multi-media receiver comprising:
an output for an IEEE 1394 Serial Bus for transmitting a transport stream to a Conditional Access Module on the bus;
a reader for reading the contents of a transport stream and identifying data which is not required for processing by a Conditional Access Module;
a stripper for stripping out at least some of the identified unrequired data from the transport stream; and
a transmitter for transmitting through the output all of the remaining data of the transport stream which has not been stripped.
According to the first aspect of the present invention, there is also provided a network of digital multi-media devices connected by means of an IEEE 1394 Serial Bus, the network comprising:
a device for transmitting a transport stream over the IEEE 1394 Serial Bus; and
a second device for receiving a transport stream over the IEEE 1394 Serial Bus; wherein
the first device includes a reader for reading the contents of a transport stream and identifying data which is not required for processing by the second device;
a stripper for stripping out at least some of the identified unrequired data from the transport stream; and
a transmitter for transmitting to the second device over the IEEE 1394 Serial Bus all of the remaining data of the transport stream which has not been stripped.
According to the first aspect of the present invention, there is also provided a method of transmitting a transport stream over an IEEE 1394 Serial Bus, comprising:
stripping out of the transport stream identifiable unrequired data so as to reduce the bandwidth of the transport stream.
Thus, since the only data to be stripped from the transport stream is that data which is positively identified as not being required by the Conditional Access Module, the stripped transport stream contains all of the data required by the Conditional Access Module. Furthermore, in practice, the stripper will be stripping out virtual channels containing broadcast program content data. The broadcast program content data takes up the most significant proportion of the bandwidth of the transport stream and, therefore, stripping out this data will have a very significant effect on reducing the overall bandwidth of the transport stream.
The present invention is applicable to any type of digital multi-media device, including devices handling audio data, video data, other multi-media data or a mixture thereof. It is particularly advantageous for digital video devices handling at least video data.
Preferably, the transport stream is an MPEG-2 transport stream and is transmitted in isochronous channels under the IEC1883 format.
A table of program specific information (PSI) is provided in the MPEG transport stream, such that unrequired parts of the transport stream can be identified for stripping.
The receiver is able to determine which streams to strip out not only from the PSI but also the user state, i.e. which program the user wishes to watch or record, etc. As receivers in general can only display one picture at a time then that is the one to be descrambled and all the others can be ignored.
According to the second aspect of the present invention there is provided a method of implementing a Common Interface Transport Stream Interface over an IEEE 1394 Serial Bus comprising:
setting up at least two isochronous channels over the IEEE 1394 Serial Bus with a Conditional Access Module;
transmitting a transport stream of the Transport Stream Interface over the first of said at least two isochronous channel to the Conditional Access Module; and
receiving a transport stream of the Transport Stream Interface over a second of said at least two isochronous channels from the Conditional Access Module.
According to the second aspect of the present invention there is also provided a digital multi-media device comprising:
a port for an IEEE 1394 Serial Bus for communicating transport stream data of a Common Interface;
means for implementing the above method;
means for transmitting a transport stream over the first isochronous channel; and
means for receiving a transport stream.
According to the second aspect of the present invention there is also provided a Conditional Access Module comprising:
a port for an IEEE 1394 Serial Bus for communicating transport stream data of the Common Interface of the Conditional Access Module;
means for setting up at least one isochronous channel over the IEEE 1394 Serial Bus with another device; and
means for transmitting a transport stream over the isochronous channel.
The Conditional Access Module may further comprise means for responding to a or the another device to set up another isochronous channel on the IEEE 1394 Serial Bus and means for receiving transport stream data from the another isochronous channel over the IEEE 1394 Serial Bus.
According to the second aspect of the present invention there is also provided a Conditional Access Module comprising:
a port for an IEEE 1394 Serial Bus for communicating transport stream data of the Common Interface of the Conditional Access Module;
means for responding to another device to set up an isochronous channel on the IEEE 1394 Serial Bus; and
means for receiving transport stream data from the isochronous channel over the IEEE 1394 Serial Bus.
Thus, in this way, it is possible for the full Transport Stream Interface to be formed over the IEEE 1394 Serial Bus and by using isochronous channels, the Common Interface may continue to send the transport stream data in its normal format without modification. Furthermore, a Conditional. Access Module may be provided which is capable of communicating transport stream data over the IEEE 1394 Serial Bus.
The transport stream on the second isochronous channel may be received by a second Conditional Access Module in which case a third isochronous channel may be set up over the IEEE 1394 Serial Bus with the second Conditional Access Module and a transport stream of the Transport Stream Interface may be received over the third isochronous channel from the second Conditional Access Module.
In this way, a transport stream can be passed consecutively from a host receiver to two Conditional Access Modules before being returned to the host receiver. This enables both Conditional Access Modules to perform different functions on the transport stream without the transport stream being passed back to the host receiver at an intermediate stage. This is advantageous over even the PC Card Implementation of the Common Interface. Of course, the method can be extended to include three or more Conditional Access Modules.
A third isochronous channel may also be set up over the IEEE 1394 Serial Bus to a remote device and the transport stream received from the Conditional Access Module may be re-routed to the remote device over the third isochronous channel.
In this way, a transport stream which has been sent from a host receiver can be re-routed to for instance a digital video recorder.
The transport stream on the second isochronous channel may be received by a remote device different from that from which the transport stream is transmitted to the Conditional Access Module.
In this way, where a transport stream is sent from a host receiver to the Conditional Access Module for processing and subsequently recording on a digital video recorder, the processed transport stream may be sent directly to the digital video recorder. This is advantageous over the PC Card Implementation of the Common Interface where a transport stream is returned to the sender.
An additional connection may be set up to the second isochronous channel with a remote device on the IEEE 1394 Serial Bus, such that the transport stream on the second isochronous channel is received additionally by the remote device.
In this way, a transport stream processed by the Conditional Access Module may be passed to more than one device without the need of any of those devices to re-route data and without taking up the additional band width required for an additional isochronous channel.
Digital multi-media devices to which the present invention may be applied include devices handling audio data, video data, other multi-media data or a mixture thereof. It may be applied particularly advantageously to digital video devices handling at least video data.
Thus, by virtue of the present invention, it is possible to preserve the higher layers of the existing DVB Common Interface as defined in EN50221, to make use of existing protocols developed for the IEEE 1394 Serial Bus, to ensure operation alongside existing products designed for use with the IEEE 1394 Bus, to ensure that the implementation allows further expansion to the DVB Common Interface standard to provide mechanisms to take advantage of the networked architecture of the IEEE 1394 Serial Bus and to ensure any extensions required to the DVB Common Interface will still be compatible with the present specification.
According to the third aspect of the present invention there is provided a method of implementing a Common Interface Command Interface over an IEEE 1394 Serial Bus comprising:
opening at least one isochronous channel over the IEEE 1394 Serial Bus; and
transmitting command data of the Command Interface over the isochronous channel.
According to the third aspect of the present invention there is provided a digital multi-media device comprising:
a port for an IEEE 1394 Serial Bus for communicating command data of a Command Interface;
means for setting up at least one isochronous channel between the port and a remote device connected to the IEEE 1394 Serial Bus; and
means for transmitting and/or receiving command data of the Command Interface over the isochronous channel.
The device may further comprise means for responding to the or a remote device on the IEEE 1394 Serial Bus to set up at least one isochronous channel with said the or a remote device and means for transmitting and/or receiving command data of a Command Interface of said the or a remote device from the isochronous channel.
According to the third aspect of the present invention there is also provided a digital multi-media device comprising:
a port for an IEEE 1394 Serial Bus for communicating command data of a command interface;
means for responding to a remote device on the IEEE 1394 Serial Bus to set up at least one isochronous channel between the port and said remote device; and
means for transmitting and/or receiving command data of a Command Interface of the remote device from the isochronous channel.
In this way, once an isochronous channel is opened on the IEEE 1394 Serial Bus, there are no particular protocol requirements for the data transmitted over that channel. Therefore, the Command Interface can transmit and receive command data over the set up isochronous channel without any need to modify the nature of the command data in accordance with the protocols used for the IEEE 1394 Serial Bus.
Preferably, at least two isochronous channels are set up between the port and the remote device to enable communication in both directions.
The present invention is applicable to any digital multi-media device including devices handling audio data, video data, other multi-media data or a mixture thereof. It is particularly advantageous for digital video devices handling at least video data.
Preferably, the various devices may be Conditional Access Modules, digital video receivers or other digital video devices.
In this way, devices connected to the IEEE 1394 Serial Bus may all make use of the functions of the Conditional Access Module.
In order to vary the bandwidth available for the command data, the host receiver or module that requires the extra bandwidth may contact the isochronous resource manager and request the extra bandwidth for this channel using IEEE 1394 protocols.
Preferably, a Common Interface IEEE 1394 Specific Transport Layer is provided between the Generic Transport Layer of the Common Interface and an IEC1883 Implementation Link Layer.
In this way, the Generic Transport Layer of the Common Interface may continue to operate in the same manner as proposed for the PC Card implementation with the lower different layers being transparent to it. The Common Interface IEEE 1394 Specific Transport Layer and the IEC1883 Implementation Link Layer act to set up the appropriate isochronous channels without any need for modification of the Common Interface.
Thus, by virtue of the present invention, it is possible to preserve the higher layers of the existing DVB Common Interface as defined in EN50221, to make use of existing protocols developed for the IEEE 1394 Serial Bus, to ensure operation alongside existing products designed for use with the IEEE 1394 Bus, to ensure that the implementation allows further expansion to the DVB Common Interface standard to provide mechanisms to take advantage of the networked architecture of the IEEE 1394 Serial Bus and to ensure any extensions required to the DVB Common Interface will still be compatible with the present specification.
According to the fourth aspect of the present invention, there is provided a method of implementing a Common Interface Command Interface over an IEEE 1394 Serial Bus comprising:
extending AV/C-CTS Protocols used for communication over the bus to include opcodes corresponding to transport objects of the Command Interface.
According to the fourth aspect of the present invention, there is also provided a digital multi-media device comprising:
a port for an IEEE 1394 Serial Bus for communicating command data of a Command Interface;
a coder for converting transport objects of the Command Interface into AV/C-CTS opcodes;
a transmitter for transmitting the AV/C-CTS opcodes through the port.
The digital multi-media device may further comprise a receiver for receiving AV/C-CTS opcodes through the port and a decoder for converting appropriate AV/C-CTS opcodes into corresponding transport objects of the Command Interface.
According to the fourth aspect of the present invention, there is also provided a digital multi-media device comprising:
a port for an IEEE 1394 Serial Bus for communicating command data of a Command Interface;
a receiver for receiving AV/C-CTS opcodes through the port; and
a decoder for converting appropriate AV/C-CTS opcodes into corresponding transport objects of the Command Interface.
In this way, the Command Interface is able to function as previously intended without modification, but can operate over the IEEE 1394 Serial Bus. Furthermore, operation of the IEEE 1394 Serial Bus is not significantly altered, since the AV/C-CTS Protocols are already in accordance with the IEEE 1394 Serial Bus and an extension of their command set will not interfere with operation, but only extend it.
Preferably, a Conditional Access Module is constructed according to the invention.
In this way, the functions of the Conditional Access Module will be available to many devices on the IEEE 1394 Serial Bus. Furthermore, the Conditional Access Module can be located in any suitable position and take any suitable form.
The present invention is applicable to any digital multi-media device including devices handling audio data, video data, other multi-media data or a mixture thereof. It is particularly advantageous for digital video devices handling at least video data.
Preferably, the eleven transport objects of the Command Interface have eleven corresponding AV/C-CTS opcodes.
In this way, each of the eleven transport objects are uniquely defined by a respective AV/C-CTS opcode, such that no further distinction need be made upon receipt of an AV/C-CTS opcode relating to the Command Interface.
Preferably, the objects of the Command Interface are encoded within the payload of the AV/C-CTS opcodes using a PC Card Implementation Transport Layer syntax.
Preferably, the AV/C-CTS opcodes are included in the header of AV/C-CTS commands and the objects of the Command Interface are encoded within the payload of the AV/C-CTS commands using a syntax at least based on the PC Card Implementation Transport Layer.
In this way, the Generic Transport Layer of the Command Interface need only consider lower functional layers in the same way as was intended for the PC Card Implementation.
Preferably, the Generic Transport Layer of the Command Interface is supported by a Common Interface IEEE 1394 specific transport layer, in turn supported by an AV/C-CTS Implementation Link Layer providing the AV/C-CTS Protocols.
In this way, the Common Interface IEEE 1394 Specific Transport Layer replaces the PC Card Implementation Transport Layer previously used, such that the Generic Transport Layer is transferred to the AV/C-CTS Implementation Link Layer with no knowledge required of its existence.
Thus, by virtue of the present invention, it is possible to preserve the higher layers of the existing DVB Common Interface as defined in EN50221, to make use of existing protocols developed for the IEEE 1394 Serial Bus, to ensure operation alongside existing products designed for use with the IEEE 1394 Bus, to ensure that the implementation allows further expansion to the DVB Common Interface standard to provide mechanisms to take advantage of the networked architecture of the IEEE 1394 Serial Bus and to ensure any extensions required to the DVB Common Interface will still be compatible with the present specification.